RECOVERY OF NICKEL USING HEAP LEACHING

RECUPERATION DU NICKEL PAR LIXIVIATION EN TAS

English Abstract

The production of nickel from a sulphide ore by heap leaching the ore by subjecting the ore to biological oxidation, separating nickel from iron, into an eluate solution, by solvent extraction or the use of an ion exchange reagent, and electrowinning ferronickel from the eluate solution.

French Abstract

Production de nickel en provenance d'un minerai de sulfure par lixiviation en tas en soumettant le minerai à l'oxydation biologique, en séparant le nickel du fer, pour obtenir une solution éluate, par extraction de solvant ou en utilisant un réactif d'échange d'ions, et par extraction électrolytique du ferronickel à partir de la solution éluatée.

Claims

Page 8
CLAIMS
1. A method of producing nickel from a sulphide ore wherein:
(a) the ore is subjected to a heap leaching process which
includes a phase of treating the ore with a first solution of
ferric sulphate carrying biological strains which promote
biological oxidation,
(b) a second solution which is produced by the leaching process
is treated with a solvent extraction or ion exchange reagent
which is selective for nickel over ferrous iron whereby the
nickel is separated from the iron and transferred in a
concentrated form into an eluate solution, and
(c) the eluate solution is subjected to an electrowinning process
to produce ferronickel.
2. A method according to claim 1 wherein a mixture of one or more of
Thiobacillus ferrooxidans, Thiobacillus thiooxidans and Leptospirillum
ferrooxidans is used in the oxidation step.
3. A method according to claim 2 wherein the Thiobacillus ferrooxidans
includes the strain TF-FC-1.

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4. A method according to any one of claims 1 to 3 wherein the phase
is continued for a period of from 2 to 10 days.
5. A method according to any one of claims 1 to 4 wherein the leaching
process includes a second phase of subjecting the ore to a biological
solution which promotes bacterial activity.
6. A method according to claim 5 wherein the second phase continues
for a period of from 100 to 300 days.
7. A method according to claim 5 wherein the second phase continues
for a period of 200 days.
8. A method according to claim 5, 6 or 7 wherein the biological solution
used in the second phase has a pH in the range of from 1,8 to 3,5.
9. A method according to claim 5, 6 or 7 wherein the biological solution
has a pH of 3,0.
10. A method according to any one of claims 5 to 9 wherein the
biological solution is a mixture of one or more of Thiobacillus

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ferrooxidans, Thiobacillus thiooxidans and Leptospirillum ferrooxidans.
11. A method according to claim 10 wherein the Thiobacillus
ferrooxidans includes the strain TF-FC-1.
12. A method according to any one of claims 1 to 11 wherein the
sulphide ore is crushed to below 6mm prior to heap leaching.
13. A method of producing nickel from a sulphide ore which includes
the step of heap leaching the ore in a first phase by treating the ore with
a first ferric sulphate and biological solution which promotes oxidation,
heap leaching the ore in a second phase by treating the ore with a
second biological solution at a pH in the range of from 1,8 to 3,5,
separating nickel from a solution, produced by the second phase, into an
eluate solution, and subjecting the eluate solution to an electrowinning
process to recover nickel.
14. A method according to claim 13 wherein the nickel is separated
from the solution using a solvent extraction or ion exchange reagent.

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15. A method according to claim 13 or 14 wherein the biological solution,
in each phase, includes the strain TF-FC-1.
16. A method of producing nickel from a sulphide ore by heap leaching
the ore by subjecting the ore to biological oxidation in a ferric sulphate
solution, separating nickel from iron, into an eluate solution, by solvent
extraction or the use of an ion exchange reagent, and electrowinning
ferronickel from the eluate solution.

Description

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Page 1
BACKGROUND OF THE INVENTION
This invention relates to the recovery of nickel from sulphide ores.
Nickel metal has been recovered from nickel sulphide bearing ore bodies
by conventional procedures wherein the ore is ground fine and the nickel
sulphide minerals are concentrated by froth flotation to produce a nickel
sulphide concentrate. The nickel sulphide minerals may be present as
pentlandite, pyrrhotite, millerite or other sulphide minerals.
The concentrate is treated further by smelting and reduction to produce
a nickel bearing matte which contains nickel, cobalt, copper and iron.
Various techniques are known for refining the matte to produce pure
metal. These include leaching, pressure leaching, hydrogen reduction,
electrowinning, the Carbonyl process, and so on. In general the refining
processes are expensive and produce nickel metal to varying degrees of
purity, roughly dependent on the cost of the process employed.
Nickel metal has many applications but its use in stainless steel is
becoming more dominant. For stainless steel, nickel metal does not need
to be as pure as for other applications and it can be used as ferronickel.
Ferronickel is produced from ores of nickel other than sulphide ores. If
however it is possible to produce ferronickel from sulphide ores then,

CA 02155050 2001-11-30
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when nickel for stainless steel is not required in a pure state, it is
possible
to avoid refining to produce pure nickel.
SUMMARY OF THE INVENTION
The invention is concerned with a process to produce impure nickel in the
form of ferronickel from sulphide ores.
The invention provides a method of producing nickel from a sulphide ore
wherein the ore is subjected to heap leaching, a solution of nickel sulphate
and iron sulphate, produced by the leaching, is treated with a solvent
extraction or ion exchange reagent which is selective for nickel over ferrous
iron whereby the nickel is separated from the iron and transferred in a
concentrated form into an eluate solution, and the eluate solution is
subjected to an electrowinning process to produce ferronickel.
The leaching process may include a first phase of treating the ore with a
solution of ferric sulphate, carrying biological strains which promote
biological oxidation.
The biological oxidation process may be carried out using Thiobacillus
ferrooxidans.

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Preferably a mixture of one or more of Thiobacillus ferrooxidans,
Thiobacillus thiooxidans and Leptospirillum ferrooxidans is used in the
oxidation step.
The Thiobacillus ferrooxidans preferably mainly consists of the strain TF-
FC-1, which is described in the specification of Australian patent No.
618177, issued on April 6, 1992, and which has been deposited at the
Australian Government Analytical Laboratories, under Accession No.
N 90/010723.
The solution which promotes bacterial activity may be adjusted in
concentration, pH or nutrients.
Finally the ore is washed and the solution separated from the ore heap.
The first leaching phase may be continued for a period of from 2 to 10
days.
The second phase may continue for a period of from 100 to 300 days,
typically about 200 days.
In the second phase the biological solution may have a pH from 1,8 to 3,5
typically about 3,0.

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The sulphide ore is preferably crushed to below 6mm.
The invention further extends to a method of producing nickel from a
sulphide ore which includes the steps of heap leaching the ore in a first
phase by treating the ore with a ferric sulphate and biological solution
which promotes oxidation, heap leaching the ore in a second phase by
treating the ore with a biological solution at a pH in the range of from 1,8
to 3,5, separating nickel from a solution produced by the second phase,
into an eluate solution, and subjecting the eluate solution to an
electrowinning process to recover nickel.
The biological solution, in each phase, preferably includes the strain
TF-FC-1.
BRIEF DESCRIPTION OF THE DRAWING
The invention is further described by way of example with reference to the
accompanying drawing which illustrates in block form a flow diagram of
the process of the invention.
DESCRIPTION OF PREFERRED EMBODIMENT
The accompanying drawing illustrates the process of the invention applied

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to the production of ferronickel from low grade nickel sulphide minerals.
The process includes the following main process steps: a series of heap
leaching phases 10A and 10B, an ion exchange step 12 and an
electrowinning stage 14.
The sulphide ore 16, which is to be treated, contains a high proportion of
the mineral pyrrhotite. It has been found that pyrrhotite reacts with ferric
sulphate in solution and ferric sulphate is reduced to ferrous sulphate:
Fe,SB + 7Fe2(S04)3 -~ 21 FeS04 + 8S
It is convenient to carry out the heap leach process in two phases 10A and
1 OB respectively. In the first phase 10A, a ferric sulphate solution is
passed
through the heap of ore to reduce pyrrhotite. This phase is usually
completed in a period of from two to ten days. This phase is important
because pyrrhotite interferes with bacterial oxidation. Ferric sulphate
solution is continuously generated in an agitated tank where bacterial
oxidation converts ferrous to ferric sulphate. Solution from the heap
carrying ferrous sulphate is recycled to the tank 20.
The activity of the ferric oxidation tank is promoted by allowing iron to
precipitate as Jarosite. Bacterial population is promoted by attachment

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to the solid. The solid precipitate is removed from solution in a settler
before it is pumped to the heap. The solid is returned to the agitated
tank.
The bacterial strain is TF-FC-1, as hereinbefore described.
In the second phase of heap leaching (10B), the ore is treated with a
solution from a large storage pond 24. The second phase can have a
duration of from 100 to 300 days, and normally about 200 days, but the
time period depends on the size of the ore according to the degree of
crushing. The ore is conveniently crushed to below 6mm, but the size
varies according to the ore type.
There is good reason to allow the pH of the solution in the second phase
to be about 3,0, but it could be in the range 1,8 to 3,5. The ore usually
contains acid consuming constituents because magnesium is invariably
present. The high pH reduces acid consumption to a very low level. The
acid consumption can be zero if enough acid is generated by oxidation
of sulphur in the ore. Remarkably, bacterial activity is good at high pH,
although the iron content of the solution is negligible. Bacterial activity
in the second phase is mainly in the heap of ore. The bacterial strain is
again TF-FC-1. These bacteria are similar to those used on refractory
gold ores where iron, nickel and sulphur dissolve to form nickel sulphate

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and iron sulphate in solution.
A portion of solution 22 is drawn from the storage pond 24 and is directed
to the ion exchange step 12. Nickel is adsorbed from solution by an ion
exchange resin which is selective for nickel. There are several ion
exchange resins which can be used for this process which are marketed
under the general grouping of chelating resins. These resins are selective
for nickel relative to ferrous iron but not ferric iron. There is very little
iron in solution. Any iron present will be ferrous iron. The problem
associated with ferric sulphate is thus largely eliminated and the chelating
resins are effective in separating the nickel from the iron in solution and
allowing the nickel to be transferred in a concentrated form into an eluate
solution 30.
The solution 30 is subjected to a known electrowinning process 14 to
produce an alloy 32 of nickel and iron. The solution, marked 34, remaining
after electrowinning still contains nickel and is reused to elute further
nickel from the ion exchange resin.

Representative Drawing